How to Lie with Meta-Analysis

Michael Constans drew my attention to a Consumer Reports article about spinal surgery. According to the article, a popular type of spinal surgery called vertroplasty (involving cementing vertebrae together) doesn’t work and should be stopped:

Despite the popularity of the procedure, the American Academy of Orthopedic Surgeons has just released a guideline [actually a meta-analysis of available data] saying it doesn’t work, and shouldn’t be used.

They reviewed all the literature about the procedure, and found two good-quality studies (randomized controlled trials) that show vertebroplasty works no better than a fake (placebo) procedure. There were no clinically significant differences in pain or disability, they say.

No significant difference means it “doesn’t work”? At best, it’s absence of evidence. And it’s not even that because we don’t know what the rest of the research suggests. The meta-analysis might have ignored thirty studies; it doesn’t say how many studies were ignored. Nor does it say what “placebo” means. Patients are interested in pain relief. Whether the pain relief is “all in their head” or whatever hardly matters. From a patient’s view, and a clinician’s view, a better comparison is a group that gets another plausible treatment or no treatment. The meta-analysis reports one study that compared vertrebroplasty to “conservative” treatment, which makes more sense.

So how come vertebroplasty has been used so often? Other experts have recommended the treatment in the past, including the United Kingdom’s National Institute for Health and Clinical Excellence, which said most people got some pain relief from the procedure.

This suggests that ignoring of evidence and poor choice of comparison group made a difference.

In this case, it probably comes down to what you mean by significant pain relief. The US surgeons set a strict definition—they said a difference in pain relief of less than 2 points on a 10-point scale was not meaningful for patients. Smaller differences in pain relief were recorded in the studies, but, say the surgeons, they were not big enough to make a real difference.

I think patients would prefer to decide for themselves what degree of pain relief is meaningful.

The surgeons say the evidence against vertebroplasty is strong, and they don’t expect future studies to overturn their recommendations.

Haha! Two studies with inferior comparison groups that failed to find a difference — and ignoring an unknown number of studies and arbitrarily raising the bar — adds up “strong evidence against”!

Still the Guideline and Evidence Report is useful. It reviews a range of treatments, provides citations (so you can look much further), and isn’t wedded to the placebo-comparison group. It includes studies with other comparison groups; the article just doesn’t mention them.

And I completely agree with the article’s conclusion:

If you’re considering any type of surgery, ask your surgeon to show you data about how likely it is to solve your problem.

And don’t take your surgeon’s word for it that such data exists.

6 thoughts on “How to Lie with Meta-Analysis

  1. Here are the results of my survey of people I know that have had the vertebrae fusion surgery. It has not relieved pain for anyone but did mean 6 months of additional suffering recovering from the surgery.

    I will never have such surgery. I will go the back muscle strengthening route instead.

  2. I had back pain so bad I could barely walk. I got Healing Back Pain by Dr. Robert Sarno. I read it. Pain went away.

    I gave it to my Brother. He was going to have surgery. After he read it, he feels so good, he is not having surgery.

    I was at a motorcycle rally in 2009. I met a guy from Texas who was miserable with back pain. I told him about Dr. Sarno. I ran into him again in 2010. He was raving about how the book worked.

    Look, it may not be for you, but I know how my back feels and I know how it helped people who were going to get surgery and then felt good enough that it was no longer an option.

  3. Often, perhaps usually, a treatment will make some people better, do nothing for others, and make some people worse.

    When a treatment makes about as many people worse as it makes better, then meta-analysts say it doesn’t work.

    But often it *does* work – for *some* people. Indeed, it might work very well indeed for them.

    The other people – for whom it makes no difference, or makes work – just need to stop using it – then everyone benefits.

    (It is just a matter of using patient response as a feedback loop.)

    Is that really so difficult to understand? – yet I can never get this point across to bio-statisticians/ epidemiologists, meta-analysts and the like…

  4. MY WIFE,CLARA, HAD UPPER AND LOWER BACK PAIN THAT WAS UNBEARABLE EVEN WITH STRONG PAIN MEDICATION……..SHE HAD SURGERY FOR A VERTEBROPLASTY PROCEDURE IN 4 PLACES AND HER PAIN VANISHED OVERNIGHT…….SHE UNDERSTANDS THAT HER SPINE WILL NEVER BE AS GOOD AS IT WAS BEFORE HER SPINAL FRACTURE AND SURGERY BUT SHE IS WITHOUT THAT UNBEARABLE PAIN………IN HER CASE WE AGREE THAT THE PROCEDURE WORKED FOR HER…….

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